A vehicle alternating-current power generator includes a Lundell rotor with a field winding and a plurality of claw-shaped magnetic pole parts in which magnetic poles different in polarity are alternately excited by the field winding in a circumferential direction. Such a vehicle alternating-current power generator is known as a conventional rotary electrical machine. PTL 1 discloses a power generator including a magnet-equipped Lundell rotor in which permanent magnets are interposed between the claw-shaped magnetic pole parts to obtain higher output density.
This type of power generator is designed with consideration given to the size of the permanent magnets and the optimization of a boss part, a disc part, and claw-shaped magnetic pole parts of the Lundell rotor core.
Accordingly, the power generator achieves both the improvement of power generation performance and the reduction of back-electromotive force.
PTL 1 describes the mathematical expression derived by determining the relationship between the magnetic flux of a permanent magnet that generates an inflexion point of output characteristics in a power generator and various constants L, W, and θ of claw-shaped magnetic pole pieces. In addition, PTL 1 describes that setting the various constants L, W, and θ would make it possible to decide consistently the residual magnetic flux density Br of the permanent magnets. Accordingly, in the power generator described in PTL 1, the magnetic poles can be set to allow the avoidance of battery overcharge and the achievement of high efficiency and high output at the same time in a universal way even with differences in specifications.
There are known magnet-embedded rotors (IPM rotor) in which permanent magnets are embedded in the outer peripheral portion of a rotor core such that NS poles alternate in the circumferential direction. The IPM rotor has become rapidly widespread due to its high torque, and installed in vehicle power generators, electric motors, and other components.
In recent years, vehicles have been formed in a slant-nose shape and their engine compartments have been reduced in size for reduction of running resistance. Along with this, the installation spaces for vehicle power generators and starters have been minimized. In this case, particular importance is placed on the capability of a starter, high-efficiency power running for assisting a vehicle in high-efficiency operation, and the performance of regenerative operation. Therefore, there has been relatively decreased demand for improvement in only sheer power generation performance, whereas attention has been focused on the power generation, torque, and regenerative ability of power generators for the case where field current becomes large in a short period of time.